SubProof1. A current WSIB clearance certificate
In Ontario, a contractor who hires a subcontractor without a valid WSIB clearance certificate can be held responsible for the premiums that sub owes WSIB (Workplace Safety and Insurance Act, section 141). A clearance certificate shows the sub is registered and in good standing on the day it was issued, and each one carries a validity period, so it has to be checked again before it runs out and before you release each payment.
Since 2013, most people who work in construction in Ontario must have WSIB coverage, including independent operators, sole proprietors and partners. A one-person crew is not exempt just because it has no employees.
2. A certificate of insurance
A certificate of insurance shows the sub's commercial general liability policy: insurer, policy number, limits and expiry date. Most general contractors ask for at least CA$2 million per occurrence and to be named as an additional insured, and many owners require CA$5 million on larger jobs. Check that the policy dates cover the whole job, not just the day the certificate was printed.
3. 306A Certificates of Qualification
Plumber is a compulsory trade in Ontario. The people doing the work need a 306A Certificate of Qualification, or must be registered apprentices working under a certified plumber.
Why plumbing needs extra care
Plumbing subs often work across many sites in a week, and small shops renew insurance at different times of year from your own policy. A lapsed liability policy matters most when there is water damage.
How often to check
Check the WSIB clearance before the first day on site and again before each payment, because a new certificate is issued for a set period and a sub can fall out of good standing between them. Check the certificate of insurance at the start of the job and at its expiry date. Keep the training and licence records with the rest of the sub's file.
Keeping it current without chasing
SubProof gives each subcontractor a private upload link, no account needed. It reads the expiry dates you enter, shows every sub as covered, expiring or expired, and emails the sub 30, 14 and 7 days before a document runs out and on the day. You get a Monday summary of who needs attention before you approve the week's payments.
This guide is general information, not legal or insurance advice. Rules change; confirm with WSIB, your insurer or your lawyer for your situation.